1. Medical Research Council Unit, The Gambia at the London School of Hygiene and Tropical Medicine, Banjul P.O. Box 273, The Gambia
2. Department of Pathology and Laboratory Medicine, University of California Los Angeles, Los Angeles, CA 90095, USA
3. David Geffen School of Medicine, University of California, UCLA, Los Angeles, CA 90095, USA
4. University College London Hospital NHS Foundation Trust, London NW1 2BU, UK
5. Department of Pediatrics, Division of Infectious Diseases, David Geffen School of Medicine, UCLA, Los Angeles, CA 90095, USA
6. Department of Clinical Epidemiology and Infection Prevention, University of California, UCLA Health, Los Angeles, CA 90095, USA